Rolls of strip steel are typically prepared at a steel manufacturing facility by longitudinal cutting of the strip from a sheet having a much greater width. The cutting tool engages the sheet on a cutting entrance side and slices through to the cutting exit side of the sheet where it causes the thus-formed strip to have an upturned, sharpened edge. Using such a strip in a continuous roll forming mill for manufacturing tubing employing induction welding would result in an unacceptable product because the extent of the welding bead formed on the inside of the tubing could not be controlled. A large or irregular interior bead could cause interference in telescopic mating of different sizes of tubing, or, where the tubing is used to convey a fluid, it could restrict the flow of a fluid through the tubing, aside from presenting an unsightly appearance. A steel strip with coined edges can be specially ordered from steel manufacturers; however, the strip now becomes "non-standard" requiring special additional manufacturing operations and resulting in a significantly increased price over a "standard" strip roll.
Tubing manufacturers have typically purchased standard strip rolls, often times cut the strip themselves to narrower widths, and removed upturned edge portions through grinding and/or cutting operations preliminary to tubing formation. Unfortunately, such operations can produce burrs, slivers or a residue of a magnetizable substance which can interfere with induction welding. In an extreme situation, a high frequency welding coil, formed by turns of copper tubing through which a cooling fluid is passed, can be destroyed by a steel particle attaching to the coil, through hysteresis heating of the particle causing melting of the tubing and release of the cooling fluid.
A tool for simultaneously rounding edges of a plurality of strips upon exit of the strips from a longitudinal severing operation, is shown in U.S. Pat. No. 3,456,473. The tool includes composite rollers on upper and vertically aligned lower shafts with the rollers including rounding rings having working surfaces for rounding both upper and lower surfaces of both edges of each strip. Other than the strip pass paths, which the strips completely fill, the upper and lower composite rollers engage each other at spaced locations throughout their coextension. The rings, which are coextensive with the rounded edges, are spaced by bushings which engage the upper and lower surfaces of the strips.
Rollers having working surfaces for providing parallel bevelled surfaces at the two edges of the strip have also been suggested. For further information concerning the structure and operation of such rollers, reference may be made to U.S. Pat. No. 2,292,810.